When a rotary screw compressor runs and loads normally but can't reach or maintain the pressure setpoint, the problem is usually one of three things: air is escaping (leaks), airflow is restricted somewhere in the system, or demand exceeds compressor capacity.
Unlike a "won't load" problem where the inlet valve doesn't open at all, here the compressor IS compressing air—it just can't keep up or can't build to full pressure.
Rotary Screw Troubleshooting
Low Pressure / Can't Reach Setpoint – Rotary Screw Air Compressor Troubleshooting
Compressor runs and loads, but pressure stays below setpoint—often caused by leaks, restrictions, or capacity issues.
Industrial systems
Field-tested diagnostics
Independent & unbiased
Safety Notice
Compressed air at system pressure (7-13 bar) can cause injury. Never search for leaks by running your hand along pressurized lines—use soapy water or an ultrasonic leak detector.
What this problem usually means
Check these first
5–10 minute checks before diving deeper
- Check for obvious air leaks—listen for hissing sounds near fittings, hoses, and connections
- Is the air demand higher than usual? (new equipment, additional users, leaky tools)
- Check inlet air filter—clogged filter reduces capacity significantly
- Verify the pressure setpoint hasn't been changed accidentally
- Check separator element differential pressure—high DP means clogged separator
- Listen for inlet valve modulating—it should be fully open when trying to reach setpoint
- Check discharge pressure reading vs. plant pressure—big difference means restriction in piping
- Look at compressor running hours vs. capacity—is it running 100% but still losing pressure?
- Check and replace downstream compressed air filters if installed—clogged filters add restriction
Common root causes
Why this happens in rotary screw compressors
Air leaks in the system
Leaks at fittings, hoses, quick disconnects, regulators, or downstream equipment. A single 3mm leak can waste 10+ CFM.
Clogged inlet air filter
Dirty inlet filter restricts airflow into the compressor, reducing capacity by 10-30% in severe cases.
Separator element clogged
High pressure drop across separator restricts discharge flow. Check differential pressure gauge—should be under 1 bar.
Demand exceeds capacity
System air demand has grown beyond what the compressor can supply. Common when facilities add equipment over time.
Inlet valve not fully opening
Inlet valve partially stuck or modulating incorrectly—compressor can't draw full capacity of air.
What NOT to do
Don't increase the pressure setpoint to "compensate" for low pressure—this masks the real problem, increases energy consumption, and can cause other issues. Find and fix the root cause instead.
Full Rotary Screw Troubleshooting Manual
Step-by-step diagnostics, root cause logic, and practical fixes for oil-injected rotary screw compressors. Save time and reduce downtime with proven methods.
- Step-by-step diagnostics for common failures
- Root cause analysis techniques
- Practical fixes with parts notes
- Works across all major brands